Process of making lithopone



Patented al-.4, 1924. i

" OFFICE.

' hours 0. DREFAHL, or LAKEWOOD,

Ann EDWARD 1L TAYLOR, or CLEVELAND, onio,

ASSIGN'ORS TO THE GBASSELLICHEMIOAL COMPANY, CLEVELAND, OHIO, A GOR- PORATION OF OHIO.

rnocnss or MAKING LITHOPONE.

Lithopone is extensively used as a paint pigment, in the manufacture of rubber goods, and for other purposes, and is manufactured in large quantities by standard processes which comprise the following Solutions of zinc sulfate and barium sulfid prepared in any suit-able 'manner are mixed in suitable proportions in the neighborhood of equimolecular proportions and Ma suitable temperature. For the purpose of improving-the physical properties of the resulting precipitate it has become cuszfl tomary to employ so-called conditioning agents. The "conditioning agent may be present naturally in one or both the zinc sulfate and the barium sulfid solutions or it may be added-thereto either before or after' so the solutions are mixed or to the resulting precipitate. The conditioning agents may perform a useful function in the precipitation of the lithopone or in the subsequent drying or mufliing operations or both. The 36 particular conditioning agent or agentsemployed and the manner in which they are used varies considerably in the manufacture of lithopone in different plants but it is generally recognized that they efl'ect o'r-govt0 ern to a large extent the physical properties of the product. Conditioning agents here tofore employed have been. inorganic salts and particularly common salt, sodium chlorid. 1

*0 have found that lithopone having particularly desirable properties can be made by the following procedure.

According to our process a barium sulfid solution is prepared in the usual manner, no

special precautions being taken in this regard. In preparingthe zinc sulfate solution, however, we are careful to have it as free as is practical from impurities. The zinc sulfate solution is prepared by standture of operation, and other Application filed March a, 1922. Serial No. 541,582.

ard procedure excepting that precautions are taken to obtain solutions as free as practical from impurities, particularly Water soluble inorganic; salts. .For th s purpose raw materials freefrom impurities are selected or'the raw materials are purified byany suitable means, such as, washing, grading, etc. or the zinc sulfate solution prepared from impure raw materials is puritied, for instance, bv fractional crystallization of either the zinc sulfate or the impuri ties, or both expedients, that is, the use of pure raw materials and subsequent purif cation of .the zinc sulfate solution.may be .employedin order to obtain a pure zinc sulfate solution.

The zinc sulfate and barium sulfide solutions are then brought together in the usual way as regardsthe manner of mixing the solutions, proportions of reagents, temperastandard conditions excepting that none of the so'-called conditioning agents heretofore employed are added to the reaction mixture;

Instead of the usual conditioning agents we employ a small amount of a solution of an alkali metal silicate. A solutionof sodium silicate'of 42, B. containing about 9 per cent, Na O and 30 per cent 310,, that is, sodium oxid and silica in the ratio of about 3.25 to 1 has been found to be suitable. It is to be understood however ,that the invention is not limited to the use of the specific sodium silicate solution defined. Solutions of different concentration and having difier ent proportions of sodium oxid and silica The sodium silicate somay be employed. lution may be added simultaneously with the mixing of the zinc sulfate and barium sulfide solutions or subsequent to the mixing of the solutions, that is, to the resulting precinitate and may be added in varying quantities, preferably in relatively small quantities. We have added sodium silicate' solution of the composition defined above in quant'ty amounting to from I to 2 per cent of the weight of the finished dry lithoponeproduct.

When the sodium silicate has been added and thoroughly mixed with thei'precipitate the product is dried, calcined in a muffle furnace, etc., according to the usual methods of making lithopone.

The properties of our product can best be.

appreciated by comparison with ordinary lithopone made by standard methods of manufacture.

The following is a tabulation of theresults of the usual empirical physical testsv on a sample of'an ordinary product and on our product.

Ordinary Our product. product.

Color dry AA l AA Color oil .I A AA obscuring power .1 90 125 Oil absorp ion..... 11.6 19 Volume 98 i 180 Fineness 98. 51 99. 9 Sun test in water. Not sunproof. Sunproof.

2 The volume of our product is '80 per cent greater than the volume of an equal weight of the ordinary product. Our product is sunproof whereas the ordinary product is not sun proof. I

Our new product approaches more nearly the properties of zinc oxid than does the ordinary product.

Under the microscope our product is seen to be much more finely divided than the ordinary product.

i The chemical composition of our produc is not materially different from the composition of the ordinary product.

The following table gives the per cent of the principal constituents of our product and the ordinary product.

Ordinary Our product. product.

Zinc sulfid 28.54 23.28 Zincoxld u. .53 1.40 Barium sulfate. 70.13 69.74

We claim: 1. Process of making lithopone WhlCh comprises, reacting upon a solution of barium sulfid with a solution of zinc sulfate,

tate. 4

2. Process of making lithopone which said zinc sulfate solution substantially free from water soluble inorganic salts other than zinc sulfate, and incorporating .an alkali metal silicate in the resulting precipicomprises, reacting upon barium sulfid with zinc sulfate,,,mix1ng the reaction product with an alkali metal silicate, and calcining the mixture.

3. Process of making lithopone which comprises, mixing a solution of barium sulfid with asolution ofzinc sulfate, adding an alkali metal silicate tothe mixed solutions, and separating the resulting precipitate. I

4. Process of making lithopone which comprises, mixing solutions of barium sulfid and zinc sulfate, said zinc sulfate solution substantially free from waterv Soluble impurities, and adding a solutionof sodium silicate to the resulting precipitate.

5. Process of making l thopone which comprises, mixing a solution of barium sulfid witha solutionof zinc sulfate and addin a solution of sodium silicate of 42.5" Be.

containing sodium oxid and silica in the ratio of 3.25 to 1 in quantity amounting to from 1 to 2 per cent of the weight of the resulting precipitate in the dry state.

6. Process of making lithopone which comprises, precipitating lithopone in the absence of any conditioning agent, and mixing the precipitate with a relatively small amount of a solution of sodium silicate prior to calcining the same. i

7. Alithopone product having relatively greatobscuring power, oil absorbing capacity, volume, and fineness and being substantially sunproof and White in both the dry state and when mixed with oil, such as may be prepared by the herein described process which comprises reacting upon a solution of barium sulfid'with a solution of zinc sulfate, and adding a small amount of a precipitate.

In testimony whereof, we afiix our signatures.

LOUIS: c. DREFAHL. EDWARD A. Tarn-on.-

solution of sodium silicate to the resulting 

